An airplane's pitch attitude is the angle defined by the longitudinal axis of the airplane and a horizontal line. Pitch attitude is an important airplane parameter that must be taken into consideration during landing approach and touchdown. Airplane pitch attitude during landing will vary according to a number of factors. For example, atmospheric disturbances, such as the presence of a wind gust, will affect pitch attitude, requiring adjustment. Pitch attitude adjustment in response to atmospheric disturbances ensures that the desired flight path angle will be maintained during landing.
During landing the pitch attitude envelope of an airplane is in part limited by the shape of the airplane. During landing flare and touchdown, as the nose of the airplane rises to increase pitch attitude, the aft section of the airplane becomes increasingly closer to the ground. The separation between the aft section of the airplane body and the ground is known as the aft body contact margin. To minimize the chance of the aft section from contacting the ground, it is desirable to not have the pitch attitude exceed a maximum value, commonly referred to as the most aft body critical flight condition. The most aft body critical flight condition defines a predetermined maximum pitch attitude that provides a required clearance between the aft section of the airplane body and the ground during landing. The required clearance is known as the aft body contact margin requirement. This requirement is in degrees and is defined by the angle between the runway and a line extending between the main landing gear of an airplane and the lowermost area of the aft section of the airplane. See FIG. 1.
In addition to a maximum value, during landing, it is also desirable that the pitch attitude not drop below a minimum value. During approach, the main landing gear and nose gear of an airplane are lowered. Because the nose gear is not designed to withstand the impact of airplane touchdown, it is crucial to land the airplane so that the main landing gear makes contact with the ground first. The separation between the nose gear and the ground when the main landing gear contacts the ground is known as the nose gear contact margin. In order to avoid nose gear first landings, a minimum pitch attitude, commonly referred to as a most nose gear critical flight condition, is defined. Landing at pitch attitudes equal to or greater than the minimum value for the most nose gear critical flight condition ensures that the main landing gear touchdown precedes the nose gear touchdown by a predetermined value. The predetermined value is known as the nose gear contact margin requirement. This requirement is also in degrees and is defined by the angle between the runway and a line extending between the main landing gear and the nose gear on the airplane. See FIG. 2.
As stated above, due to atmospheric conditions and other parameters, the pitch attitude of an airplane during landing will vary. Sometimes, the pitch attitude will increase to a large value, lowering the aft section of the airplane dangerously close to the ground during approach and touchdown. In some instances, the aft body contact margin requirement may be violated, causing the aft section of the airplane body to contact the ground, resulting in damage to the airplane.
These issues have been addressed by the landing attitude modifier (LAM) disclosed in U.S. Pat. No. 5,823,479. When the trailing flaps of an airplane are in a landing flap detent position, the LAM switches on and positions lift-generating surfaces, such as the flaperons, ailerons, or spoilers, to improve the nose gear contact margin and the aft body contact margin during an airplane's landing. As mentioned above, however, the LAM uses these devices with the trailing edge flaps in a landing detent position, so drag is increased during the approach segment of flight. Increased drag will increase airplane noise during approach in two ways. First, increased engine thrust will be needed to offset the drag increase. Increased engine thrust will increase approach noise. Secondly, increased drag is the result of an uneven lift distribution caused by flaperon deflections used to control attitude. The uneven distribution will cause approach noise generated by the airframe to increase.
The increased approach noise will cause an unfavorable environmental impact on communities surrounding the airport, and will also increase the Approach Noise certification level as defined by Federal Aviation Regulations, Part 36. Increased certified Approach Noise levels may restrict airplane operations at certain airports with an unfavorable impact.
A system and method is thus needed to overcome noise-related issues of the existing LAM systems and methods.